Breast magnetic resonance imaging (MRI) has been used for preoperative evaluation in women with breast cancer for almost two decades, but is still the subject of clinical controversy. While preoperative breast MRI is known to detect additional cancer, the impact of this on preoperative work-up, surgical treatment and outcomes is not clear. A major question is whether detecting additional cancer leads to more aggressive work-up and surgery (mastectomy instead of breast conserving surgery) without any concomitant benefits. Prior studies have not compared population-based use of breast MRI with standard imaging modalities in relation to breast cancer surgery and important outcomes, such as re-excision, subsequent tumors, and mortality. Expanding use of breast MRI necessitates a large-scale assessment of these outcomes to inform clinical practice guidelines and to understand potential benefits and harms for women with breast cancer. This proposed research will: 1) examine the influence of preoperative breast MRI on additional cancer detection, preoperative work-ups and the relation with mastectomy vs. breast conserving surgery;2) compare breast MRI with mammography 1 ultrasound in relation to re-excision, subsequent tumor events, and mortality;3) assess utilization of preoperative breast MRI nationally and in subgroups of women, such as those with increased breast cancer risk;4) estimate population-wide impacts of preoperative breast MRI use through Markov models of utilization and outcomes. We will use newly established linkages of the national Breast Cancer Surveillance Consortium (BCSC) registry data with Medicare and Group Health claims data to address these aims in a unique and novel way. These data will leverage existing resources by augmenting health care utilization data with risk factor, co morbidity, clinical assessment, and pathology information. The BCSC data consists of a large population of women primarily from community settings, enabling us to examine subgroups of women, such as those with ductal carcinoma in situ, dense breasts or family history of breast cancer, and to have greater generalizability than previous studies. Our overall objective is to provide critical evidence about the effectiveness of preoperative breast MRI compared to standard imaging modalities to inform current practice protocols, women's decision-making and health care policies. In this era of new technologies and health care reform, identifying if and when advanced modalities benefit patients is of the utmost importance to both patients and resource allocation efforts. PUBLIC HEALTH RELEVANCE: Using magnetic resonance imaging (MRI) to evaluate breast cancer prior to breast cancer surgery has been shown to detect additional areas of cancer compared to mammography. Because of this additional detection, some women may undergo further preoperative work-up and mastectomy in one or both breasts, instead of lumpectomy. These treatment decisions impact a woman's experience, and may impact her prognosis. Currently, it is not clear whether preoperative breast MRI for women with breast cancer improves outcomes, such as reduced re-excision rates in the case of lumpectomy, fewer recurrences, and lower mortality. In the midst of this uncertainty, breast MRI is being used more frequently, although the use seems to vary by region and type of facility. This increasing use will bring the unanswered questions about preoperative breast MRI even more to the forefront of breast cancer care and women's decision making. This proposal seeks to quantify the benefits and potential harms of preoperative breast MRI and to understand how women are likely to be impacted by its expanding use.